The present invention relates to optical microphone/sensors.
Several different types of optical microphone/sensors have been developed. One of these uses optical fibers and optical fiber connectors to connect between a light source and a photodetector and the optical fibers at one of their ends and between the fibers and an optical head situated near an acoustical membrane at their other ends. These microphones, of high quality, are expensive due to the high prices of optical fiber and optical connectors, as well as the high cost of the technological process used in their production.
Another type of optical microphone utilizes integral construction, wherein the source of light and the photodetector constitute part of the optical head and there are no optical connectors and optical fibers. The optical head is produced by molding. Such optical microphones are of relatively low cost, compared to that of common electric microphones. Although these microphones possess specific advantageous characteristics, they have a disadvantage in comparison with optical fiber microphones: they are sensitive to radio frequency interference (RFI).
The problem of RFI in microphones becomes even more acute in cellular telephones, as the size of such devices is diminished. Due to the fact that a telephone microphone is distant from the speaker""s mouth, its acoustic characteristics are declining.
In order to overcome this problem, in for example cellular telephones it is required to bring the microphone closer to the user""s mouth, namely, in this instrument to locate the microphone at the telephone flipper and, by doing so, to bring the microphone closer to the mouth during use.
RFI becomes the main problem in cellular telephones or like apparatus when, for example, the microphone is distant from the telephone apparatus and the connection lines between the microphone and the apparatus become long enough, e.g., several centimeters. In such a case, the RFI value becomes so strong that the use of a distantly located microphone becomes impossible. This phenomenon is typical of electric microphones and, in part, also to integral optical microphones.
It is therefore a broad object of the present invention to improve the sensitivity, as well as the acoustic and other characteristics of an optical microphone/sensor.
It is a further object of the present invention to provide a low-cost optical microphone with no electrical connections or lines between the microphone and the device to which it is connected, and that is not susceptible to RFI.
According to the invention, there is therefore provided a head for an optical microphone/sensor, including first and second light guides, said first light guide being coupled at an input end to a source of light and having an output end portion for transmitting light onto a membrane, said second light guide having an input end portion for receiving light reflected from said membrane and an output end coupled to a photodetector, said output end and input end portions each having an upper face and side surfaces and being disposed in close proximity to each other and optically separated along adjacent surfaces, characterized in that in order to utilize maximum light energy transmitted through the light guides by said light source, reflected by said membrane and received by said photodetector, at least one of said faces or surfaces is configured to extend along one or more planes which differ from the plane including the axes of the transmission of the light energy emitted from said light source and received by said photodetector.